1. Field of the Invention
The present invention relates to a radiographic video processing device, a radiographic video capturing device, a radiographic video capturing system, a radiographic video processing method, and a program storage medium.
2. Related Art
Recently, radiation detectors sometimes referred to as, for example, “electronic cassettes”) such as flat panel detectors (FPDs) are being implemented, in which a radiation sensitive layer is disposed on a thin film transistor (TFT) active matrix substrate and with which radiation can be converted directly into digital data. Radiographic image capture devices that employ such radiation detectors and capture radiographic images expressing irradiated radiation are also being implemented. Radiation conversion methods used by radiation detectors employed in such radiographic image capture devices include indirect conversion methods, in which radiation is first converted into light with a scintillator and then the converted light is converted into electrical charges (charges) with a semiconductor layer, such as a photodiode, and direct conversion methods in which radiation is converted into charges with a semiconductor layer such as amorphous selenium. There are various materials that can be used in the semiconductor layer for each method.
Such radiographic image capture devices include devices capable of performing video image capture in addition to capturing still radiographic images. Utilizing such a radiographic image capture device enables displaying the state inside the body of a patient as a video image (fluoroscopic image) on a display device in real-time, thereby enabling an endoscope to be passed to an affected site while observing the video image, and performing treatment of the affected site while observing the affected site through the endoscope. Further, using such radiographic image capturing devices enable, for example, Interventional Radiology (IVR) in which the distal end of a catheter to which various instruments are attached is passed to an affected site and medical treatment is performed by manipulation of the catheter from outside of the body.
As an example of technology relating to such types of radiographic image capture devices capable of performing both still image capture and video image capture, Japanese Patent Application Laid-Open (JP-A) No. 2008-83031 discloses an electronic cassette type radiation detector provided with a sensor array including plural sensors that detect incident radiation. The electronic cassette type radiation detector includes a connection portion for a detachable additional function module, and includes a selection means for switching image capture modes in a selectable state between a still image capture and a video image capture by connecting the additional function module.
Moreover, JP-A No. 2005-287773 discloses an image capture device including: an area sensor; an image capture mode setting means that selects one image capture mode from plural predetermined image capture modes; a correction means that performs computation using image capture output from the area sensor and an offset output; and a control means that controls operation of the area sensor and the computation by the correction means according to signals from the image capture mode setting means.
Technology such as that disclosed in JP-A No. 2006-158728 is proposed as technology relating to video image capture.
JP-A No. 2006-158728 proposes technology in which an imaging subject is irradiated with radiation from a radiation irradiation section at a specific cycle, a subject image is detected by a photoelectric conversion circuit based on the irradiated radiation and offset images are also periodically acquired, and a radiation irradiation cycle of the radiation irradiation section and a read cycle of the subject image from the photoelectric conversion circuit are controlled according to changes in the periodically acquired offset images. Thereby, accurate offset correction of the imaging subject image is performed directly after the start of image capture when fluctuations in offset occur due to alternately performing the offset image capture and the imaging subject image capture, and capturing of the subject image is successively performed at a high frame rate after the offset has stabilized.
Moreover, since there is a need to shorten the reading time for videos, when charges according to radiation dose are read, the reading time can be shortened by technology in which plural lines are read at the same time using a binning read method that reads charges of plural lines at the same time, such as in the technology disclosed in JP-A No. 2007-68014. JP-A No. 2007-68014 proposes that voltage supplied from a vertical drive circuit to a transfer section is varied according to the number of pixels that are read at the same time, in order to prevent an increase in an electrical offset component and a decrease in output voltage from pixel output amplifiers.
In a radiographic image capture device of this type, plural pixels, each including a sensor portion that generates charges according to irradiated radiation, and a switching element that reads charges generated in the sensor portion, are disposed in a matrix formation. In such a radiographic image capture device, ‘binning’ may be performed, in which charges generated by plural adjacent pixels in the radiation detector are combined and read, in order, for example, to reading out image data obtained by image capture at high speed, or to enhance image capture sensitivity.
However, in cases in which an image captured by a radiographic image capture device capable of performing video image capture such as that described above is displayed on a display device, in situations in which the number of pixels whose charges are combined by binning (hereafter also referred to as the binning number) is increased while performing image capture in the radiographic image capture device, there is an issue that disruption may occur for several frames' worth of displayed images from the point in time of the increase.
Feed-through noise with mutually reverse polarity occurs at timings when the switching elements provided to the radiation detector of the radiographic image capture device are switched ON and when the switching elements are switched OFF.
The charges read by each of the switching elements of the radiation detector are converted to voltage while being integrated by an amplifier at a predetermined cycle, and are then converted to digital values by an analog-to-digital (A/D) converter. Consequently, the influence of feed-through noise is normally prevented since the two feed-through noises of reverse polarity to each other are integrated by the amplifier, and as a result each feed-through noise is cancelled out.
However, before and after an increase in the binning number in the radiation detector, the wiring capacity of signal wirings for outputting charges read by the switching elements suddenly changes, resulting in a sudden change in the manner in which feed-through noise occurs. It is thought that the disruption in the display image occurs as a result that cancelling out of the feed-through noises is not able to follow such change.
In the technology described in JP-A No. 2006-158728, no consideration is given to unstable video image quality when switching to increase the number of lines that are read at the same time in a binning reading method, leaving room for improvement.
In the technology described in JP-A No. 2007-68014, reduction in dynamic range and deterioration in sensitivity characteristics are prevented by varying the voltage supplied to the transfer portion from the vertical drive circuit according to the number of pixels that are read at the same time. However, as above, no consideration is given to unstable video image quality when switching to increase the binning number, leaving room for improvement.